2009 Glen Rosa fire and the 1917 Halifax Harbour explosion

If we begin to think of wildfires as an energy release, rather than smoke, ash and community evacuations, there is no reason to be surprised by their destructive effects.

Typically government describes forest fires as hectares burned, dollars spent, resources deployed and, lately, persons evacuated. The Ministry of Forests used to report the values lost in its annual reports, but that has ceased. The media may add some figurative language; usually some reporting tropes and pathetic fallacies that invest the fire with menace and mystery, especially when the reporting gets repetitive or the human interest angle dries up.

Just as predictable, is everyone’s surprise at the destruction left by these wildfires. Wildfires are profoundly disturbing events; particularly when people have to tally up their possessions and witness life’s certainties come under assault. But should we be surprised at their destructive capacity?

If we begin to think of wildfires as an energy release rather than smoke and ash they become more comprehensible: albeit not any less shocking. Let’s take the recent Glen Rosa fire in the B.C. Okanagan and look at it from the perspective of energy released.

The fire consumed roughly 300 hectares of severely drought-affected and ingrown Interior dry belt forest over three days. If we estimate the volume of wood (fuel) likely present in the stands as 300 cubic meters per hectare before the fire, and assume a conservative 20 percent rate of consumption—with the large material at 20 percent moisture content—the fire was releasing energy, mostly heat, at the rate of 936 gigajoules net energy per hectare. That gives us a total amount of energy released during the fire of 281,000 gigajoules. The average Canadian home has a heating requirement of approximately 100 GJ/yr. The city of Smithers, B.C. consumes 351,000 GJ of natural gas each year.

For a more interesting reference let’s compare this energy released as a net energy equivalent of TNT. That works out to .25 kilotons of explosive per hectare. The Glen Rosa fire then was equivalent to the energy that could be released from 75 kilotons of TNT. The historic Halifax Harbour explosion detonated the equivalent of 3 kilotons of TNT. Viewed in terms of energy, the Glen Rosa fire was equivalent to 25 Halifax Harbour explosions. Even if we consider that the 1917 munitions blast occurred in ten seconds, and the Glen Rosa release took three days, it is still easy to understand the destruction involved in the Okanagan fire. Viewed this way the effects of the wildfire are not surprising at all.

This comparison looks at one of the immediate consequences of the burn. But combustion and its instantaneous effects aren’t the only products of the Glen Rosa wildfire. What will be the more diffuse impacts of this fire’s contribution of green house gas into the atmosphere? Using the same general assumptions as before; the estimated volume of total emissions released, calculated at 1422 tonnes of carbon dioxide equivalent per hectare, is 431,000 tonnes. Included in that are 500 tonnes of fine particulate matter, 24 tonnes of sulfur dioxide and 90 tonnes of nasty soot: all of which have direct health effects on humans. These calculations ignore a host of other direct, indirect and downstream effects such as altered hydrology, green house gas emissions from decomposition and so on.

Another way to make sense of the emission volumes is to consider if we taxed them under the BC Carbon tax laws. It would cost $6.3 million in carbon taxes to plug the carbon leak caused by just the Glen Rosa fire.

As of July 31, there had been a total of nearly 49,000 ha of wildfires in B.C. The combined carbon footprint of these fires has been 81-million tonnes CO2e. This exceeds the entire annual provincial human-caused carbon footprint of about 61-million tonnes CO2e.

If we consider that at least 15 million hectares of B.C.’s forests have severe health problems that are contributing to the build up of fuels in our forests; applying these kinds of calculations to the woods reveals a tremendous force gathering momentum across the landscape. We have every reason to be distressed; but no real reason to be surprised by the destructive potential.

John Betts,
Executive Director
Western Silvicultural Contractors’ Association
Ph: 250-229-4380